Duster sagging

The springs are bad and getting worse day by day. Better off replaceing them.

Air shocks are not the best idea, coil overs are way more expensive than new springs. I bet if you look arond a auto part store, you'll find long shackles. You can do those. Cheap and easier to do than add a leaf, which actually isn't a bad idea, just more labor invloved and sucks to do just as bad as the shackles.